It is known that certain plastic materials have found application in the ovenware field. For example, polymethylpentene has been used for injection molded trays which can be used in the preparation of foods. The poly-(aryl ether sulfone) from 2,2-bis(4-hydroxyphenyl)propane ("Bisphenol-A") and 4,4'-dichlorodiphenyl sulfone (UDEL Polysulfone, sold by Amoco Performance Products, Inc.) is also employed in food handling applications. Although UDEL Polysulfone, for example, gives excellent results in a number of applications; the ultimate polymer composition for this type of application must possess utility over the wide ranges of conditions and of demands which are encountered in the provision of cook-in containers; and must yield ovenware which can be used in either thermal ovens or microwave ovens.
In addition to the obvious necessity for a material which can withstand the temperatures met in the heat source used for cooking, a material must provide a unique combination of a number of characteristics before ovenware fabricated from it can be successfully employed in the preparation of food. The composition must have good microwave properties. It must be able to undergo severe thermal shocks; ovenware prepared from it must be capable of going from conditions of extreme cold to high temperatures in relatively brief periods of time. The material must have good hardness, impact and drop strength and possess high tensile and flexural strength. It must also be resistant to boiling water, food acids and fats, and to adverse effects from immersion in detergents under dishwasher cycles.
In the area of food related properties the material must impart to the ovenware fabricated from it, resistance to staining by a wide variety of foodstuffs. It must provide a surface affording good antistick properties, ready releasability for the food which it contains. It must not emit or give off any volatile matter, and it must not have any extractable constituent. And, in addition to meeting all of the foregoing requirements, articles prepared from it must present a pleasing and generally uniform appearance in order to be marketable.
Plastic compositions with an overall good combination of properties, yielding satisfactory ovenware articles and based on p-oxybenzoyl polyesters are described in Duska, et al., U.S. Pat. No. 4,626,557.
Recent work in these laboratories resulted in the preparation of a host of novel inexpensive hydroquinone poly(iso-terephthalates) containing p-hydroxybenzoic acid moieties. The molar ratios of a group of these materials is shown on the attached triangular diagram FIG. I and is described in the Definition of the Invention. The polymers melt in the range of from about 300.degree. to about 420.degree. C. Of particular interest are the polyesters falling into the two areas A and B of FIG. I. The latter products were found to form a stable oriented melt phase at 340.degree. to 400.degree. C.; the melt phase is tractable and can be extruded below its decomposition temperature to form high modulus and high strength fibers, films and molded articles displaying a good retention of properties at high temperatures. Materials filled with 30 weight percent of glass fibers have heat distortion temperatures of from about 240.degree. to about 280.degree. C., under a load of 264 psi. Moreover, the polymers grouped in areas A and B have crystallization temperatures in the range of from 300.degree. to 340.degree. C.; and their crystallization rates are at least 1000 counts per minute and up to 3500 counts per minute as measured by X-ray techniques. The polyesters are the subject of commonly assigned U.S. patent application entitled "Hydroquinone Poly(iso-terephthalates) Containing Residues of p-Hydroxybenzoic Acid", Ser. No. 412,785, filed concurrently with the present application, now U.S. Pat. No. 5,097,001.
Our investigations have also shown that alloys having markedly improved molded properties are obtained when the copolyesters hereinabove described are blended with wholly aromatic polyesters comprising units (V), (VI), (VII), and (VIII) in well-defined proportions. In view of the fact that alloys of materials having ordered structures are expected to show reduced properties, the discovery was highly surprising and totally unexpected. Improved characteristics included improved blister resistance, which is poorly understood and not predictable. The novel alloys are the subject of commonly assigned U.S. patent application entitled "Polymer Compositions Having Improved Molding Characteristics", Ser. No. 451,366, filed concurrently with the present application now abandoned.
It was now unexpectedly discovered that the attractive properties of the hydroquinone copolyester-based alloys are maintained in composites comprising talcs of well-defined characteristics. The novel composites meet the stringent requirements of cook-in containers and are suitable for the fabrication of demanding ovenware articles.